Known is a machine for digging under pipelines, containing symmetrically located end effectors made in the form of rotary posts with the driven spiral mills with the right-hand direction of blade turn for the mill located on the left side in the direction of the machine movement and left-hand direction for the right mill, and the breast located behind the spiral mills (USSR Auth. Cert. #1263765, cl. E02F 5/06, 1986). However, in view of the fact that the breast is made common for both end effectors and fastened on their posts, the self-digging of the machine under the pipeline is impossible. As the posts rotate around the horizontal longitudinal axes with the spiral mills moved out from under the pipeline, the posts do not fall within the trench clearance limits, thus requiring digging of the latter using additional mechanisms or manually. Besides, with the mentioned direction of the blade turns the mills rotation proceeds in such a way, that the upper blades are moving in the direction opposite to that of the machine movement, which results in the soil throwing over the breast with the increase of the mills rotation speed.
Known is a machine for pipeline digging, incorporating posts with the driven spiral mills mounted on telescopic shafts (USSR Auth. Cert. # 1198166, cl. E02F 5/02, 1985). However, the design of the telescopic shaft, of the drive for its extension and assembly of its mounting on the post, is complex, unreliable, not capable of standing high loads and with a large diameter of the pipeline, cannot practically fall within clearance limits of the post. Besides, the absence of breasts lowers the effectiveness and performance of the spiral mills.
Known is a machine for digging under the pipeline which incorporates the frame, symmetrically located end effectors made in the form of posts placed on both sides of the pipeline and mounted on a frame with the capability of forced rotation around the horizontal longitudinal axes, and driven rotors mounted on the lower ends of the posts by means of vertical shafts located on both sides of the pipeline, and mounted on the frame travelling unit of the stepping type (USSR Auth. Cert. # 24882, cl. E02F 5/08, 1976). In view of the large dimensions of the rotors and of the posts rotation around the horizontal longitudinal axes with the rotors moved out from under the pipeline, they do not fall within clearance limits of the trench, thus, firstly not permitting the machine to be moved over the pipeline with the rotors brought apart, for instance for by-passing an insurmountable obstacle, and secondly, requiring digging up the trench for the machine mounting-dismantling. In order to prevent the rotors jamming under the pipeline, the axes of the posts rotation should be maximum close to the vertical plane of the pipeline symmetry, thus not permitting the travelling unit to be placed between them, thereby increasing the machine overall dimensions. The absence of the breasts adversely affects the quality of the trench bottom under the pipeline. The upper end faces of the rotors coming closer to the pipeline lower surface for its cleaning from the soil, increases the probability of the pipeline damaging. Besides, the stepping travelling unit has comparatively large overall dimensions, complex design and is complicated to operate. Here, the average speed of the machine movement is more than 2 times lower than the speed of rotors feed to the soil face, thus lowering the machine efficiency and increasing the power consumption, as a result of idle running of the rotors during the machine stoppage.
The closest to the claimed machine is the machine incorporating a frame, with the end effector made in the form of a post located to the side of the pipeline and mounted on a frame with the capability of forced rotation around the vertical axis, the driven part mounted on the post lower end and placed to the side of the latter with the horizontal location of its longitudinal axis, the breast located in the direction of the machine movement behind the driven part, and the cutter made in the form of a ring segment and located in front of the breast, as well as the travelling unit and idle wheels mounted on the frame for the machine movement over the pipeline. Unlike the claimed machine, in the known machine the vertical axis of the post rotation is located in one plane with the longitudinal axis of the driven part, which is made in the form of a chain bar, the breast and cutter are fastened to the frame, while the drive travelling unit is made in the form of bull-wheels mounted at an angle to each other (USSR Auth. Cert. # 562625, cl. E02F 5/10, 1977). In the known machine, as a result of the driven part being made in the form of a chain bar which just undercuts the soil mass, without loosening it, a high traction force is required in order to remove the soil from under the pipeline. Here, the travelling unit cannot provide the sufficiently high traction force, as it is impossible to press the wheels to the pipeline surface with a large force because of a small area of contact of the wheels with the pipeline. For the same reason, it is impossible to increase the machine weight. This results in the known machine having a low efficiency, providing digging under pipelines of a small diameter and to a small height. As the breast and the cutter are fastened to the frame, self-digging is impossible, and mounting-dismantling of the breast and the cutter are required during the machine mounting and taking off. Besides, in rotation of the post to move the chain bar from under the pipeline, the machine center of mass is shifted towards the post, this impairing the steadiness of its position on the pipeline. The removal of the soil for under the pipeline to one side, requires increasing the depth of the pit which is not rational in technical terms. The known machine requires changing the wheels of the drive travelling unit for its mounting on pipelines of different diameters, thus making its operation more difficult.
The closest to the claimed device, is the known caterpillar travelling unit incorporating a frame and a caterpillar chain which includes the plate traction chains mounted on the frame on the tension and drive sprockets, rigid elements protruding beyond the contour of the caterpillar chain middle part, and flexible supporting elements coupled with the rigid elements. Unlike the claimed unit, in the known device the rigid elements are made in the form of outer plates of the traction chains, whereas the flexible supporting elements are coupled with the rigid elements by extended slots with the capability of displacement within the length of the slots in order to eliminate the tension of the flexible supporting elements. Here, the caterpillar chain includes the rubber element mounted on the traction chains for accommodating the support-traction loads (USSR Patent # 1831456, cl. B26D 55/24, 1993, FIG. 7). In the known device the flexible supporting elements do not accommodate the support-traction loads because of elimination of their tension, but serve as anti-skidding elements for the rubber element. The presence of the rubber element, first of all, lowers the reliability and fatigue life of the device, especially when the travelling unit is used on the pipelines with bitumen insulation because of the bitumen mastic sticking to the surface of the rubber element and impossibility of cleaning it, and secondly, increases the resistance to the displacement of the travelling unit through losses for the rubber element deformation. Thirdly, it makes the device design more complicated.
The advantages of replacement of the insulating coating of the operating pipelines performed on the design elevations of the pipelines in the trench mostly without interruption of the operation of the latter, have long ago become obvious for the experts who began taking certain efforts for its practical implementation. However, one of the reasons for which such a technology has not yet found due acceptance in practice, is the fact that the construction machinery used in practice, as well as the technical means which are not used in practice, but are known from the state-of-the-art publications, do not offer a satisfactory solution for the problem of digging under pipelines. The most preferable approach is performance of work to replace the pipeline insulating coating during the continuous displacement of the entire system of the appropriate technical means, without the use of fixed supports for allowing the pipeline to rest on the trench bottom. Here, higher requirements are made of the technical means for digging under pipelines, which are met by the above technical means to an even smaller degree. In this case, the device for digging under the pipeline should be capable of fulfilling its function during its continuous displacement with the speed which is equal to the speed of displacement of the entire system (preferably 150 to 100 m/h); here the above means should make the minimum impact on the pipeline, eliminating its damage. In addition, the means for digging under the pipeline should have minimal overall dimensions in the direction along the pipeline, in order to reduce the length of the unsupported section of the pipeline to such an extent as to avoid or minimise the use of the mobile means for the pipeline support. Here, the above means should provide a rather considerable height of digging (about 0.8 m) with a broad range of preferably large diameters of the pipelines, so as to enable the operation of the means of the pipeline cleaning and insulation. It is exactly the absence currently of such means of digging under pipelines which largely prevents a wide practical introduction of the technology of replacement of the insulating coating of the operating pipelines in the trench without the use of supports for allowing the pipeline to rest on the trench bottom. Thus, the inventors faced a challenge still unsolved in a manner suitable for practical application, despite the numerous attempts at solving it over many years.